This invention relates to an implantable microstimulator or neural prosthesis powered by an operative in response to an externally applied signal. In particular, the invention relates to a device responsive to an input signal having a power component and a control component wherein the device output is controllable in accordance with encoding associated with the input signal.
Autonomic problems occur in areas of the bowel, bladder and respiratory systems following spinal cord injuries. Methods for managing these problems are active areas of medical research. An important approach is the use of electrical stimulation or neural prosthetics. A particular direction in the application of electrical stimulation is the use of a small, fully implanted microstimulator that is activated with radio frequency (RF) energy.
Conventional approaches employ various techniques for controlling the amplitude and duration of the applied electrical stimulation. Such techniques suffer from problems associated with the inefficient coupling of the input power to the device. As a result, systems have been developed which are designed to provide a selective level of power output. Such systems are often inefficient and expensive to implement. In addition, such systems do not provide for versatile controls. For example, in some systems the signal level may only be varied in accordance with the duration of the applied input signal. Other systems may allow for variable signal strength and duration but require adjustments be effected by electromechanical coupling, i.e., by the application of external magnetic fields.
Also, conventional devices have limited capability to deliver relatively high currents over prolonged application cycles. Such systems may not be satisfactory for use in connection with bowel stimulation, which may require application of relatively high currents during a treatment period for as long as 30 minutes.